Modern tree harvesting operations generally comprise equipment such as a land vehicle with large-diameter wheels or a pair of crawler tracks. The vehicle is generally equipped with a multi-function tree processing apparatus mounted at the end of an articulated boom. The tree processing apparatus can fell a tree, delimb it and severe the tree trunk into sawmill logs and pulpwood in a single sequence of operation. The logs are thereafter picked up and forwarded near a forest road by log porters.
These modern operations are efficient in the sense that logs are transported from stump sites to roadside in only two machine manipulations. This is a commendable improvement over the multiple sequences of a conventional practice comprising felling, skidding, piling, delimbing, piling again, severing and stacking in cords along a trucking road.
Examples of these multi-function tree processing apparatus are disclosed in U.S. Pat. No. 4,766,939 issued on Aug. 30, 1988 to Torsten Forslund, and in U.S. Pat. No. 5,219,010 issued on Jun. 15, 1993 to Peter Eriksson.
The introduction of these multi-function tree processing apparatus in the forest industry has made conventional delimbing machines less wanted. Examples of conventional delimbing machines are described in U.S. Pat. No. 4,276,918 issued on Jul. 7, 1981 to Roger Sigouin, and in U.S. Pat. No. 4,382,457 issued on May 10, 1983 to Raymond M. Hahn. In the first example, a sliding boom is mounted atop a track type excavator. The sliding boom is used to delimb, to cut the top portion of full length trees, and to pile those trees awaiting further processing by a severing machine. In the second example, the machine is movable on wheels to drive it near piles of felled trees. The machine has an articulated boom, a pair of sliding delimbing blades, a tree trunk severing saw, and a log sorting mechanism with two cradles to separate sawmill logs from pulpwood. The sorted logs are periodically handled out of the cradles by the articulated boom and piled in a location where a porter may thereafter carry these logs to a roadside site.
In both examples, the delimbing machines are limited to work near piles of trees accumulated by forwarders or by a feller-buncher machine. Thus the additional cost of operating the delimbing machines renders a forestry operation less profitable than the use of a multi-function tree processing apparatus as firstly described.
In other typical forestry operations, a variety of delimbing attachments have been developed to operate in combination with an articulated boom of a log loader. For examples U.S. Pat. No. 4,899,794 issued Feb. 13, 1990 to Thomas E. Hamby, Jr. and U.S. Pat. No. 5,406,997 issued Apr. 18, 1995 to Tim Davison, disclose a first type of tree delimbing device where the tree is drawn through a pair of limb stripping blades by the grapple of a log loader.
A second type of tree delimbing attachment for use in cooperation with an articulated loader boom is illustrated in U.S. Pat. No. 4,167,960 issued Sep. 18, 1979 to Allan J. Wildey, and in U.S. Pat. No. 5,293,914 issued on Mar. 15, 1994 to Thomas H. Hudson. In both devices, there is provided a pair of delimbing blades and a tree topping mechanism.
A common inconvenience with both types of delimbing attachments of the prior art is that the operation of the log loader is dedicated to a single function of operating the delimbing attachment. The loader-delimber combination works from a pile of trees which has been previously accumulated by forwarders, by skidders or by a feller-buncher machine. Furthermore, a severing machine is subsequently required to cut the trees into logs of appropriate lengths. Therefore, this type of operation is also relatively expensive as compared to multi-function apparatus of the present-day trend.
Although the multi-function tree processing apparatus are very efficient, the investment in a mobile machine with an articulated boom and a tree processing apparatus mounted thereon requires the obtainment of large wood harvesting contracts where a machine can work around the clock for several months per year.
This type of operation is generally not feasible for small and medium size forestry contractors where the tree processing machines are only periodically utilized. Hence the small and medium size forestry contractors must contrive to remain competitive using conventional machinery.
In another aspect of a present-day forestry operation, the small and medium size forestry contractors generally have one or more log porters. The small and medium size contractors referred to herein are those contractors having few employees, and even the self-employed woodcutters.
Log porters are generally of the articulated type with a front drive portion having an engine and a cab for an operator, and a rear log carrying portion having a loader boom. The front and rear portions are normally connected by a steering joint. A porter is generally equipped with large-diameter wheels such that it can carry heavy loads on rough terrains. The machines are particularly agile in moving about through harvested forest land to gather logs from one pile of logs to the next.
Log porters have traditionally been working exclusively on carrying logs out of the forest, and a return on investment therefor has been limited to this activity alone.